Proceedings of The Physiological Society

Dietary regulation of bovine ruminal UT-B urea transporter expression

G. Stewart1, E. Scriven1, C. Smith1, N. Simmons2

1. Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom. 2. School of Cellular and Molecular Biosciences, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, United Kingdom.

Ruminants, such as cattle, need to recycle nitrogen through the process of urea nitrogen salvaging (UNS) in order to maintain nitrogen balance (1). The process of UNS requires large amounts of urea to pass into the gastrointestinal tract and previous studies have suggested that this occurs through ruminal facilitative UT-B urea transporters (2). In this study we have investigated the effect of dietary intake on bovine ruminal UT-B urea transporter expression. Ruminal tissue samples were obtained from 6 adult cows, 3 which had been fed an ordinary forage diet (RO) and 3 which had been fed a concentrate diet (RC). Using a 32P-labelled full-length bUT-B cDNA probe, northern analysis detected no difference in the level of the 3.7kb bUT-B transcript between ruminal RNA samples from the two diets (NS, Unpaired T-Test). In contrast, western analysis of ruminal protein samples using a recently characterized bUT-B antibody detected significant differences between the two groups. For example, a 36 kDa bUT-B signal representing unglycosylated bUT-B2 was significantly greater in RC compared to RO ruminal protein (P<0.05, Unpaired T-test). Finally, using 10µM sections of methanol-fixed ruminal tissue, immunolocalization studies showed that while the bUT-B signal was found predominantly in the stratum basale in RO samples, it was found mainly within cells of the stratum granulosum in RC samples. Our results therefore provide strong evidence that ruminal UT-B urea transporter protein expression is altered by dietary intake. Since ruminal microflora, short-chain fatty acids and pH are altered by concentrate feeding, further work on these factors are required to understand the cellular basis of UT-B expression.